Just how desperate is Microsoft Corp. (MSFT) to get customers to relinquish their death grip on its nearly decade-and-a-half old operating system, Windows XP? It's now offering customers $100 USD to get rid of their old Windows XP PC -- although some restrictions do apply.

The caveat is that you have to trade in your computer at a Microsoft Store, and you have to buy a new Windows 8.1 machine that costs $599 USD or more (limiting the maximum discount is roughly 16 percent).

The good news is that most of the laptops and desktops at Microsoft stores are relatively new, so it's unlikely that Amazon.com, Inc. (AMZN), Newegg, and other online retailers will be able to offer a better deal, on average.

Microsoft has previously offered a $50 USD gift card for those who traded in XP machines. By contrast the new deal is simply a direct discount, redeemable instantly off your purchase.

Windows XP computers are still found in vast quantities in many parts of the world. While they're now in the minority in the U.S., Microsoft's figures suggest that when the April termination of support for the platform rolls around 65 percent of users in China -- the world's most populous nation -- will still be using Windows XP. Unfortunately there's not enough $100 USD discounts to solve that dilemma.